Detergent composition for use in hard water



Patented Dec. 24, 1946 DETERGENT COMPOSITION FOR USE IN HARD WATERFrederick C. Bersworth, Verona, N. J.

No Drawing. Application June 9, 1944,

Serial No. 539,595

' 4 Claims. 1

This invention relates to water softening agents and more particularlyto water softening agents for use in association with alkali metal-fattyacid soap compounds.

One object of the invention is to provide a water softening agent which,in addition to being'reactive as a deionization agent towards the usualwater hardening compounds, is also reactive as an electrolyte-carrierand is compatible and miscible in all proportions with alkalimetal-fatty acid soap compounds, in their hydrous or anhydrous state,thereby to form detergent compositions utilizable in hard, saline orhard-saline water.

Another object is to provide a deionization and electrolyte-carryingagent compatible with alkali metal-fatty acid soap compounds in thesolid or liquid phases or in aqueous solution.

Still another object is to provide an alkali metal sa t of an aliphaticamino-polycarboxylic acid possessing in aqueous solution deionizationproperties towards water hardening salts and electrolyte-carryingproperties towards neutral salts such as strong electrolytes and whichis miscible with alkali metal-fatty acid soap compounds in allproportions either in their dry or liquid phases or in aqueous solution.

Other objects will be apparent as the invention is more fullyhereinafter disclosed.

In accordance with these objects I have discovcred that the acid-alkalimetal salts of the aliphatic amino-polycarboxylic acids arenon-electrolytes towards the alkali metal-fatty acid soap compounds andare electrolyte-carriers towards strong electrolytes normally reactiveto insolubilize or salt-out the said soap compounds in aqueous solutionas well as being strong deionizing agents and that these saidacid-alkali metal salts of the said amino acids are miscible in allproportions with alkali metal-fatty acid soap compounds in their hydrousor anhydrous forms.

Heretofore in the art, as exemplified by Munz Patent No. 2240.957 issuedMay 6, 1941, the use of the aliphatic amino-polycarboxylic acids and thealkali metal salts of said acids as a deionization agent in hard watersin association with water soluble soap compounds has been disclosed. Ihave found, however, that whereas these acids and the alkali metal saltsof these acids are excellent deionization agents for hard waters theyare not utilizable in association with water soluble soap compounds, ofthe alkali metal-fatty acid type for the reason that the amino acidreacts with the alkali metal-fatty acid soap compounds to insolubilizethe same as free fatty acids while the alkali metal salts of these aminoacids, in

. 2 aqueous solution, hydrolyze and liberate free caustic alkali whichis a strong electrolyte operating to salt-out the said alkalimetal-fatty acid soap compounds from aqueous solution, when present inany great concentration therein.

I have found that the addition of enough of the free amino acid or ofthe alkali metal salt of said acid to even moderately hard water todeionize the said water is generally sumcient to cause extensiveinsolubilizing of the alkali metalfatty acid soap compounds and thatneither the amino acid nor the alkali metal salt of the acid is misciblewith the alkali metal-fatty acid soap compounds in their solid or liquidanhydrous phases or in concentrated aqueous solution. This limits theutility of these amino compounds materially as such compounds may not beadded to or incorporated in concentrated hydrous soap solutions or mixedwith anhydrous soap compounds to form bar, flake, powder products orliquid soap compositions.

After extensive investigation I have discovered that in aqueous solutionthe amino acid, for example, ethylene diamine tetracarboxylic acid, andcaustic alkali form a plurality of acid-alkali metal salts having morethan two (2) but less than four (4) of carboxylic acid groupsneutralized by the alkali, which acid-alkali metal salts are stable inaqueous solution. These acid-alkali metal salts are not recoverable fromaqueous solutions as anhydrous compounds, and in aqueous solution arenon-electrolytes towards alkali metal-fatty acid soap compounds and actas strong electrolyte-carriers towards neutral electrolytes, such assodium chloride, and sodium sulfate, which normally react toinsolubilize or salt out alkali metal-fatty acid soap compounds. Inaddition these acid-alkali metal salts of the amino acid are highlyreactive towards basic oxides, hydroxides and carbonates to deionize thesame and are completely miscible in all proportions with alkalimetal-fatty acid soap compounds (hydrous 1 or anhyrous) to formdetergent compositions therewith that are utilizable with all types ofhard, saline and hard-saline water.

As one specific embodiment of the present invention, but not as alimitation thereof, the invention will be described as it has beenadapted with respect to the acid-alkali metal salts of ethylene diaminetetracarboxylic acid, one of the plurality of amino polycarboxylic acidsdisclosed in the above identified Munz patent, it being understood,however, that any of the aliphatic amino-polycarboxylic acids known inthe art and disclosed in said Munz patent as an equivalent auaesa 3 forethylene diamine tetracarboxylic acid, which have more than two (2)carhoxyiic acid groups therein, may be substituted for ethylene diaminetetracarboxylic acid without departure from the present invention.

Ethylene diamine tetracarboxylic acid may be prepared in a number ofdiflerent ways. It is best prepared by the method disclosed and claimedin my co-pending application Serial No. 491,669 filed June 21, 1943,which is assigned to the same assignee as the prevent invention. By thepractice of the invention of said copending application I first obtainan aqueous solution consisting principally of the tetra alkali metal(sodium) salt of ethylene diamine tetracarboxylic acid. The free aminoacid is recovered from this solution by acidifying the solution with astrong mineral acid, such as HCl or H2804, to a pH approximating pH 1.6.At this DH the free amino acid is of low solubility in the highlyconcentrated sodium chloride or sulfate solution and precipitates out asa white crystalline powder. The free amino acid is insoluble in coldwater and may be washed free of the mother liquor with cold pure wateron a suction filter.

In accordance with the present invention, the aqueous solution of theacid alkali metal salt of the free acid is prepared in the followingmanner:

One molar weight of the free acid and three molar weights of a causticalkali (NaOH or KOI-I) are added to one liter oi pure water and themixture is heated for an extended time interval until a clear solutionis obtained. The pH of the clear solution is adjusted by additions ofthe free acid or of caustic alkali thereto, as may be required, toobtain a pH within the range 7 pH to 9.5 pH.

My experiments have indicated that the pH of the acid-trisodium salt ofethylene diamine tetracarboxylic acid approximates 7.4 in aqueoussolutions of this concentration. The pH of the tetrasodium salt of thisacid approximates 10.5 and the pH of the acid-disodium salt approximates3.8. For the purposes of'the present invention, namely, to provide adeionizing and electrolyte-carrying agent which is compatible withalkali metal-fatty acid soap compounds in their solid and liquid phasesand miscible therewith in aqueous solutions, I have found that any ofthe acid-sodium salts which in molar strength solution have a pH withinthe range 7 to 9.5 are satisfactory but I prefer to closely approximatea.

pH of about 8.

In the production of detergent compositions consisting of a mixture ofalkali metal-fatty acid soap compounds and the acid-alkali metal salt ofthe present invention, the amount of the deionizing andelectrolyte-carrying acid-salt of the present invention that is added tothe soap compounds varies with respect to the hardness and to the amountof electrolyte present in the water in which the detergent is to beused. As an illustration, in hard water of the type known generally asfrom moderately hard to hard, I have found that about (based on theweight of the soap compounds) of the above acid-sodium salt of ethylenediamine tetracarboxylic acid, calculated from the estimated dry weightof the salt in the molar weight solution obtained above, is suiiicientto soften the water so that the soap compounds are freely functionabletherein as a detergent.

An aliquot portion of the molar weight aqueous solution of theacid-trisodium salt of ethyl- "be added to soap stock, solid or liquid,and following thorough admixture therewith may be formed into bar,flake, powder or liquid soap products by any of the methods heretoforeemployed in the art. 4

Where soap solutions of bar, flake, powder or liquid soap productsutilizable in very hard water, or in water containing large amount ofstrong electrolytes, are desired, the amount of the acidtrisodium saltof ethylene diamine tetracarboxylic acid incorporated therein may beincreased to as high as 25% without detrimentally effecting thedetergent properties of the soap compounds in the water. In general, Ihave found 10% (by weight) of the acid-trisodium salt to be adequate inmost very hard water and in water containing moderate amounts of strongelectrolytes such as sodium chloride or sodium sulfate. In hard andsaline water, such as sea water, I have found that 20 to 25% (by weight)of the acid-trisodium salt is preferable.

It is believed apparent, from the above disclosure that manymodifications and departures may be made in the above disclosedinvention without essential departure therefrom. In place of ethylenediamine tetracarboxylic acid, for example, any of the aliphatic aminopolycarboxylic acids heretofore identified as deionization agents forhard water, may be substituted without departure from the presentinvention, particularly those having more than two carboxylic groupsattached directly to amino nitrogens which, in aqueous solution. formacid-alkali metal salts having a pH within the range 'I to 9.5 ashereinabove disclosed with respect to the acid-alkali metal salts ofethylene diamine tetracarboxylic .acid. A1l,of these amino acids and thealkali metal salts of these acids react similarly to ethylene diaminetetracarboxylic acid insofar as forming acid-salts of the type hereindescribed that are stable only in aqueous solution. None of theacid-alkali metal salts of these acids have heretofore been eitherrecognized or utilized as deionization agents or have been produced withsuflicient purity to permit the study and identification of theirparticular chemical properties, such as herein describe As analternative procedure to the practice hereinabove disclosed, theacid-trialkali metal salt of the present invention may be produced inthe following manner:

To an aqueous solution of the tetrasodium salt of ethylene diaminetetracarboxyllc acid, containing one molar weight of the salt per liter,heated to elevated temperatures up to the boiling point of the solution,ethylene diamine tetracarboxylic acid is added, until a pH within therange 'I to 9.5 is obtained. In this reaction one molar weight of thefree amino acid normally is sumcient to lower the pH of the solutionfrom a pH of about 10.5 to a pH of about 8, which is approximately thepI-I of the trisodium salt of ethylene diamine tetracarboxylic acid. Thesolution thus obtained is then diluted to obtain a molar weight solutionof the acid-trisodium salt of ethylene diamine tetracarboxylic acid forconvenience in handling and in calculating the allquot portions thereoffor use in mixing with soap compounds or soap solutions.

Various other organic and inorganic acids may be employed in place ofthe ethylene diamine tetracarboxylic acid in the above alternativeprocedure without essential departure from the present invention, thestrong electrolyte-carrying properties of the acid-trisodium salt beingsuch as to render innocuous any neutral electrolyte salts formed by theuse of such acids.

Various other modifications and departures will occur to those skilledin the art and all such are contemplated as may fall within the scope ofthe following claims.

What I claim is:

1. A detergent composition for use in hard waters, in water containingstrong electrolytes, and in hard and saline waters, said compositionconsisting of a mixture of alkali metal-fatty acid soap compounds and 5%to 25% of the acid-trialkali metal salt of ethylene diaminetetracarbomlic acid.

} metal salt of ethylene diamine tetracarboxylic acid.

4. A detergent composition for use in hard and saline water,saidcomposition consisting of a mixture of alkali metal-fatty acid soapcompounds and about 20 to of the acid-trialkali metal salt of ethylenediamine tetracarboxylic acid.

FREDERICK C. BERSWORTH.

